Heavenly Dust

Tiny particles add up to bright lights

By J. Alex Knoll

The sun sets a few minutes after 8:00 this week, revealing a triumvirate of bright planets in its wake. Venus, Mars and Saturn continue their weeks-long dance above the western horizon. Over the next week, watch as Mars and Saturn jockey for position just above brilliant Venus. The three planets are their tightest on Saturday, all within five degrees of one another.

As these three planets set in the west around 10pm, Jupiter rises in the east. With Venus gone and the waning crescent moon not rising until early morning, Jupiter, at magnitude –2.7, is the brightest light in the heavens. By midnight old Jove has climbed into the southeast, and as dawn approaches he is high in the south.

While Jupiter is the second-brightest planet, it is hands-down the largest, bigger than some stars and large enough to swallow more than a thousand earths — more massive than all the solar system’s other planets and moons combined. For such a large planet, Jupiter spins like crazy, faster than any other planet. Comprised almost entirely of gaseous elements, this giant would literally float apart were it not for its frenzied rotation, leaving behind a smaller — still 10 times the size of earth — orb of dense solids.

If you’re up before dawn one of these moonless August morns, look for the zodiacal light, a pearly glowing pyramid of light stretching from the western horizon and tilting to the left, running through the constellations of the zodiac. What you’re seeing is sunlight reflecting off tiny interplanetary specks of dust that orbit the sun, just like you might see dust floating through the air before a sunny window.

This year’s Perseid meteor shower peaks around midnight August 12-13. As earth nears the debris-strewn trail of comet Swift-Tuttle, the source of the Perseids, errant particles are already caroming against the atmosphere, igniting into the fireballs we see as meteors.